The present invention relates to a new method of producing vehicle steering wheels, and which is particularly suitable for producing steering wheels with a covering of valuable material, e.g. brier; and to steering wheels produced using such a method.
In the automotive industry, various types of wooden steering wheels are produced using various methods. One of these consists in producing rings of shaped laminated wood, possibly with a brier veneer, which are fitted to a supporting structure of the steering wheel. Though relatively cheap to make, steering wheels produced this way are unsatisfactory in appearance and normally cannot be made from the same type of wood used for other interior parts of the vehicle (e.g. door panels, dashboard, etc.). Another known method consists in veneering a polymer (typically polyurethane) layer of the steering wheel structure with one or more layers of brier. While providing for a fairly attractive appearance, this method is relatively expensive and, from the manufacturing standpoint, involves serious problems as regards adhesion of the wood veneer to the underlying polymer support, on account of the different chemical and physical properties of the two materials.
The same drawbacks in terms of cost or poor appearance also apply to other known methods of producing wooden or wood-veneered steering wheels.
It is therefore an object of the present invention to provide a method of producing vehicle steering wheels, which, unlike the above known methods, provides for achieving a highly attractive appearance, in particular matching the other interior parts of the vehicle, and which at the same time is straightforward and cheap to implement.
According to the present invention, there is provided a method of producing vehicle steering wheels, in particular steering wheels with a covering of valuable material; characterized by comprising the steps of:
forming a supporting structure of a steering wheel, the structure having at least one outer cover layer of a polymer material of predetermined density;
forming at least one pair of curved preformed half-shells shaped and sized to fit, facing each other, on opposite sides about a predetermined portion of said structure, so as to define a substantially continuous, tubular shell covering said structure portion;
winding at least one layer of cloth, impregnated with a polymer resin, about said structure portion and over said outer cover layer of the structure;
applying said at least one pair of preformed half-shells to said at least one layer of impregnated cloth to form said substantially continuous, tubular shell covering said structure portion;
producing a polymerization reaction of said polymer resin to bond said preformed half-shells to each other and, via the interposition of said at least one layer of cloth, to said outer cover layer of said structure.
Said step of forming said supporting structure of said steering wheel preferably in turn comprises a step of forming in said outer cover layer of said structure at least one recessed portion permitting thermal expansion of said polymer material.
The present invention also relates to a vehicle steering wheel comprising a supporting structure of said steering wheel, the structure having at least one outer cover layer of a polymer material of predetermined density; and characterized by also comprising at least one pair of curved preformed half-shells fitted, facing each other, on opposite sides about at least one corresponding predetermined portion of said structure, or about the whole of the structure, so as to define a substantially continuous, tubular shell covering said structure portion; at least one layer of cloth, impregnated with a polymer resin, being wound about said structure portion, over said outer cover layer of the structure, and being interposed radially between said outer cover layer of said structure and said preformed half-shells.
Said supporting structure of said steering wheel preferably comprises, in said outer cover layer of polymer material, at least one recessed portion permitting thermal expansion of said polymer material.
The present invention therefore provides for producing, at relatively low cost, highly functional vehicle steering wheels with a covering of valuable material, e.g. real wood, and in particular of the same type of wood used for other interior parts of the vehicle (door panels, dashboard, etc.) to achieve a highly attractive effect.
The layer of impregnated cloth interposed between the polymer (e.g. polyurethane) supporting structure and the preformed half-shells (e.g. made of multilayer material with a sandwich structure of wood and cloth impregnated with polymer resin) ensures strong adhesion of the half-shells to each other and to the structure, despite the chemical incompatibility and poor natural adhesion of wood and polyurethane (or similar polymers). Moreover, the recessed portion in the outer cover layer of the structure permits thermal expansion of the polymer material of the outer cover layer without radially compressing the preformed half-shells fitted to the outer cover layer, thus preventing thermal expansion of the structure from deforming, warping or even detaching the half-shells.
Moreover, beneath or together with the layer of impregnated cloth, the steering wheel structure may be wound with an electric resistance heating element, which, being substantially incorporated in the cloth layer, does not raise the overlying layers. The present invention therefore provides for producing, in a straightforward, low-cost manner, heated steering wheels with a wood veneer or covering of other valuable material, and of flawless finish.